1. Field of the Invention
The present invention relates to a magnetic sensor whose operating layer is made of a group-III nitride semiconductor.
2. Description of the Background Art
It is known that magnetic sensors such as a Hall element and a magnetoresistive effect element whose operating layer is made of a semiconductor material exhibit higher sensitivity with increasing carrier mobility of the semiconductor material used. Therefore, conventionally compound semiconductors such as InSb and InAs which exhibit high electron mobility have been used for the operating layer of the magnetic sensor (refer to, e.g., “Physical properties of InSb single-crystal thin film and magnetic sensor application”, IEEJ Transactions on Electrical and Electronic Engineering E, Vol. 123, No. 3 (2003), pp. 69-78). For example, the Hall element in which Hall effect of a thin-film of InSb or InAs is utilized is extensively used as a magnetic sensor of DC brushless motor.
There is also known a magnetic sensor whose operating layer is made of a group-III nitride semiconductor having a wide bandgap (refer to, e.g., Japanese Patent Application Laid-Open Nos. 2003-060255 and 2006-080338). This magnetic sensor has an advantage that a characteristic change is hardly generated even at a high temperature although it is inferior in the carrier mobility and sensitivity to the magnetic sensor for which InSb or InAs is used. Particularly, Japanese Patent Application Laid-Open No. 2006-080338 discloses that a magnetic sensor whose operating layer having an AlxG1-xN/GaN (0.3<x≦0.5) heterostructure can well operated at 300° C. or more (in a range of 0° C. to 800° C.).
There is also known a technique of suitably controlling a donor concentration in forming an N-type group-III nitride semiconductor layer (refer to, e.g., Japanese Patent Application Laid-Open No. 2005-035869).
As described in Japanese Patent Application Laid-Open No. 2003-060255, in the case of the magnetic sensor for which InSb or InAs is used, there is widely known a drawback that the magnetic sensor cannot be used at a high temperature because of temperature dependence of a Hall voltage measured under a condition of constant magnetic flux density.
Japanese Patent Application Laid-Open No. 2003-060255 specifically discloses only the fact that the magnetic sensor whose operating layer is made of the group-III nitride semiconductor operates in a temperature range not more than 200° C. There is disclosed no specific fact that the magnetic sensor functions well at a high temperature range not lower than 300° C. or no requirement to realize the magnetic sensor well operated in the high temperature range not lower than 300° C. That is, Japanese Patent Application Laid-Open No. 2003-060255 does not disclose the magnetic sensor well operated in the high temperature range not lower than 300° C. The same holds true for Japanese Patent Application Laid-Open No. 2006-080338.
On the other hand, in Japanese Patent Application Laid-Open No. 2006-080338, a range of x≦0.3 is excluded in the AlxG1-xN/GaN heterostructure constituting the operating layer of the magnetic sensor. For the case of the AlxG1-xN/GaN heterostructure, because the electron mobility in the range of x≦0.3 is larger than that in the range of 0.3<x≦0.5, the higher-sensitivity magnetic sensor which is well operated at 300° C. or more is realized if the range of x≦0.3 is utilized.